The present invention relates to a front end shock absorbing apparatus for a wheeled vehicle having a brake. Although the invention is especially suited for a motorcycle, it may be applied without significant modification to three and four wheeled motor vehicles and also to manually propelled vehicles such as bicycles.
It is desirable and well known to provide shock absorbers between the wheels and frames or chassis of wheeled vehicles such as motorcycles. The purpose of the shock absorbers is to provide a smooth ride for the vehicle operator and passengers by preventing impacts resulting from irregularities in the road surface from being transmitted from the wheels of the vehicle to the frame. Although the wheels are vertically displaced by such road surface irregularities, compression of the shock absorbers prevents the frame from being displaced by a corresponding amount.
The shock absorbers are generally tubular telescopic units which incorporate coil springs as well as hydraulic fluid chambers. Upon compression of the shock absorbers, the springs compress and also hydraulic fluid is displaced through a flow restriction from one chamber to another to absorb shocks.
Another such shock absorbers function in a satisfactory manner during constant speed operation of the motorcycle, a problem has remained heretofore unsolved during braking operation, especially abrupt braking under emergency conditions. Upon braking of the motorcycle, inertial forces cause the front end of the frame to depress relative to the front wheel and compress the front shock absorbers. Under extreme braking conditions the shock absorbers are compressed to a maximum extent. This prevents the shock absorbers from performing their intended function of absorbing road shocks, and seriously degrades the steerability of the motorcycle. This lack of steering control occurs at a time when accurate and responsive steering are most needed, and constitutes a major safety hazzard.
Several proposals have been made in the prior art for overcoming this problem, but they cannot be considered entirely satisfactory. A typical example, which constitutes the closest known prior art, is disclosed in U.S. Pat. No. 3,989,261. This reference discloses a shock absorption system which is operated in a normal manner when the motorcycle is not being braked. However, in response to a sensed braking condition, a valve is closed which blocks communication between the fluid chambers in the shock absorbers and places the shock absorbers in a condition of hydraulic lock, thereby preventing compression of the shock absorbers during braking.
Whereas this prior art system constitutes an improvement in steerability and safety during braking, it operates in an on-off manner and presents an abrupt transition from normal shock absorption to hydraulic lock at a particular sensed degree of braking force, thereby surprising and confusing the operator under emergency conditions. Other prior art systems of similar type are disclosed in Japanese application disclosure Nos. 50-97042, 51-23921, 52-16748 and 52-19850.